Re: NFSv4/pNFS possible POSIX I/O API standards

[Andreas Dilger <adilger@clusterfs.com>]

On Nov 28, 2006  05:54 +0000, Christoph Hellwig wrote:
> What crack do you guys have been smoking?

As usual, Christoph is a model of diplomacy :-).

> On Mon, Nov 27, 2006 at 09:34:05PM -0700, Gary Grider wrote:
> > >readx/writex - scattergather readwrite - more appropriate and 
> > >complete than the real time extended read/write

IMHO, this is a logical extension to readv/writev.  It allows a single
readx/writex syscall to specify different targets in the file instead of
needing separate syscalls.  So, for example, a single syscall could be
given to dump a sparse corefile or a compiled+linked binary, allowing
the filesystem to optimize the allocations instead of getting essentially
random IO from several separate syscalls.

> > >statlite() - asking for stat info without requiring completely 
> > >accurate info like dates and sizes.  This is good
> > >for running stat against a file that is open by hundreds of 
> > >processes which currently forces callbacks
> > >and the hundreds of processes to flush.

This is a big win for clustered filesystems.  Some "stat" items are
a lot more work to gather than others, and if an application (e.g.
"ls --color" which is default on all distros) doesn't need anything
except the file mode to print "*" and color an executable green it
is a waste to gather the remaining ones.

My objection to the current proposal is that it should be possible
to _completely_ specify which fields are required and which are not,
instead of having a split "required" and "optional" section to the
stat data.  In some implementations, it might be desirable to only
find the file blocks (e.g. ls -s, du -s) and not the owner, links,
metadata, so why implement a half-baked version of a "lite" stat()?

Also, why pass the "st_litemask" as a parameter set in the struct
(which would have to be reset on each call) instead of as a parameter
to the function (makes the calling convention much clearer)?

int statlite(const char *fname, struct stat *buf, unsigned long *statflags);


[ readdirplus not referenced ]
It would be prudent, IMHO, that if we are proposing statlite() and
readdirplus() syscalls, that the readdirplus() syscall be implemented
as a special case of statlite().  It avoids the need for yet another
version in the future "readdirpluslite()" or whatever...

Namely readdirplus() takes a "statflags" paremeter (per above) so that
the dirent_plus data only has to retrieve the required stat data (e.g. ls
-iR only needs inode number) and not all of it.  Each returned stat
has a mask of valid fields in it, as e.g. some items might be in cache
already and can contain more information than others.

> > >The website is at
> > >http://www.opengroup.org/platform/hecewg/
> > >We in the HECIWG would welcome putting forth any NFS related ...

Strange, group is called HECIWG, website is "hecewg"?

Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.